Absorption chillers are designed to generate cooling (chilling) effect by means of generating chilled water which can be used to extract heat from an air flow (e.g. in an air conditioning system). Absorption chillers create a chilling effect by going through a complete absorption-refrigeration cycle. The simultaneous heat and mass transfer of the refrigerant to and from its mixture with the absorbent is the main mechanism of producing the chilling effect in an absorption chiller. The absorbent in the system should have a great tendency towards the refrigerant by dissolving it readily under the operating conditions of the system. The absorption process will make it possible for the system to work at sub-atmospheric pressures (between 0.01-0.1 atm for a water-based absorption chiller) leading to the evaporation of the refrigerant at much lower temperatures than its normal boiling point.
In absorption chillers, the need for an electricity consuming part (i.e. a compressor) to pressurize the refrigerant is addressed through the use of an appropriate absorbent. Latent heat is consumed for the evaporation of the refrigerant, which provides a means of chilling. The low pressure in the evaporator provides the benefit of easy evaporation of the refrigerant (i.e. liquids evaporate easier at lower pressures), thereby making the system capable of producing a chilling effect at low temperatures. However, the very low pressure of the evaporator makes the condensation process of the vapor phase (in order for the cycle to be continued) more challenging. This is where an efficient absorbent is needed to thoroughly absorb the refrigerant vapor (which previously has been cooled by releasing latent heat to a cooling water stream) and to change it back into the liquid phase.
Like any other chemical/physical system, absorption chillers have their own drawbacks and limitations. Certain factors such as the crystallization of the absorbent in the system, or the heat loss from different compartments of the system, can make the system deviate from the ideal performance predicted by thermodynamic-based models. The benefits and drawbacks of conventional absorption chillers are described as follows.
Benefits of an Absorption Chiller:
                Low electricity cost—The only electricity consuming part in the system is a relatively small pump, which is used to circulate the absorbent-refrigerant mixture within the system. This fact makes absorption chillers an ideal choice for countries which do not have well developed infrastructures for the generation of electricity.        It is a closed system in which almost no refrigerant (commonly water) is wasted.        Ability to work in both dry and humid climates.Drawbacks:        
Water-lithium bromide (LiBr) salt is a commonly used refrigerant-absorbent (working) pair in absorption chillers. LiBr is a very efficient absorbent for water refrigerant due to its high hygroscopicity. LiBr, which as a pure salt has a melting temperature of 552° C., can absorb water to a high enough degree such that it becomes completely dissolved in the water it has absorbed. [1]
However, absorption chillers working with LiBr absorbent can only operate within a relatively narrow range of the concentration of LiBr in water. The process is impaired if the solution of LiBr in water is either too concentrated or too dilute. On the one hand, a very low amount of water is insufficient to keep LiBr in the liquid phase due to the high melting point of LiBr (552° C.), causing the absorbent to crystallize out of the liquid working pair [2]. On the other hand, a very high amount of water (too dilute of a solution) will completely cover and solvate the Li+ cations and Br− anions, disturbing the capability of the system to work continuously and efficiently. A narrow (˜5%) change in LiBr concentration in the water (from ˜57% LiBr/43% water in the diluted stream to ˜62% LiBr/38% water in the concentrated stream) is typically required to produce an acceptable amount of cooling load while preventing the solution from being too concentrated or too dilute.
Another drawback of LiBr salt as an absorbent is its corrosiveness, necessitating the use of costly corrosion inhibitors and copper piping. Due to the corrosive nature of LiBr and the involved control procedures needed to avoid its crystallization within the system, there is a need for absorption chillers having less problematic absorbent materials compared with LiBr.